The steering of the forward strut in the hydrofoil "Canard" ship configuration or the aft strut in the hydrofoil "airplane" ship configuration is required in order to economically maneuver the hydrofoil ship.
The steering or rudder strut also provides structural support to a hydrofoil arrangement. Previously, the strut and foil have been steered as a unit.
However, advanced marine ships of the hydrofoil type will be larger and faster than the present versions and accordingly various problems occur. For instance, the steering of the strut with integrally connected foil assembly increases the steering torque requirement, overtaxes the hydraulic system and increases the steering mechanism's vulnerability to floating log collisions.
A prior attempt has been made to resolve the problem by swiveling a fairing around a cylindrical post or inner structural strut member with a series of bearings. This solution created other problems, such as:
1. The diameter of the post and bearings required to support the foils and the fairing loads is such that the thickness and chord of the fairing become very large, and increase drag and weight.
2. Flutter problems cannot be resolved, and
3. A HARD STOP FOR THE FAIRING MUST BE PROVIDED FOR, WHICH IS AN ADDITIONAL FEATURE AND ADDITIONAL COST AND WEIGHT.
Thus the steering concept must meet the requirements of
A. PROVIDING STRUCTURAL SUPPORT TO THE FOIL AND OTHER NECESSARY COMPONENTS UNDER THE MOST SEVERE LOADING CONDITIONS EXPECTED DURING OPERATION;
B. PROVIDE FOR A RUDDER OF NARROW THICKNESS FOR MINIMUM DRAG;
C. PROVIDE FOR A HARD-STOP TO PREVENT CATASTROPHIC FAILURES;
D. PROVIDE A STEERING AXIS AT APPROXIMATELY 20% OF CHORD FOR STABILITY, AND
E. PROVIDE FOR STEERING ANGLES IN THE 12.degree. - 15.degree. RANGE.